Re: [PATCH v6 1/4] openat2: new OPENAT2_REGULAR flag support

Aleksa Sarai <[email protected]> Fri, 17 Apr 2026 01:15:42 +1000

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On 2026-04-16, Dorjoy Chowdhury <[email protected]> wrote:
> On Thu, Apr 16, 2026 at 7:52 PM Jori Koolstra <[email protected]> wrote:
> >
> > On Sat, Mar 28, 2026 at 11:22:22PM +0600, Dorjoy Chowdhury wrote:
> > > diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h
> > > index 50bdc8e8a271..fe488bf7c18e 100644
> > > --- a/arch/alpha/include/uapi/asm/fcntl.h
> > > +++ b/arch/alpha/include/uapi/asm/fcntl.h
> > > @@ -34,6 +34,7 @@
> > >
> > >  #define O_PATH               040000000
> > >  #define __O_TMPFILE  0100000000
> > > +#define OPENAT2_REGULAR      0200000000
> > >
> >
> > I don't quite understand why we are adding OPENAT2_REGULAR inside the
> > O_* flag range. Wasn't this supposed to be only supported for openat2()?
> > If so, I don't see the need to waste an O_* flag bit. But maybe I am
> > missing something.
> >
> 
> Yes, OPENAT2_REGULAR is only supported for openat2. I am not sure if I
> got a specific review to not add OPENAT2_REGULAR in the O_* flag 32
> bit range. But as far as I understand, for the old open system calls
> we can't easily add new O_* flags as the older codepaths don't strip
> off unknown bits which openat2 does. It's not easy to add new O_*
> flags for the old open system calls since that could break userspace
> programs. So I guess it's okay to add OPENAT2_REGULAR in the 32 bits
> range anyway? (Also lots of code paths take 32bit flags param right
> now and those would need changing to take uint64_t instead but this is
> of course not a reason to not add the new flag outside of the 32
> bits).

Oh, I didn't notice that this wasn't mentioned here, we had a separate
discussion about it in a thread with Jori and I must've assumed we
discussed it in both. (My brain is also really not wired up to read
large octal values easily.)

While it is hard to add new O_* flags (hence OPENAT2_REGULAR), it's not
/impossible/ (Jori has a patch for OPENAT2_EMPTY_PATH that is safe to
add to O_* flags because of some fun historical coincidences).

I would have a slight preference towards segregating the bits, ideally
at the top end but even 1<<31 would've been nice. Then again, I'm not
too fussed either way to be honest...

-- 
Aleksa Sarai
https://www.cyphar.com/

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